I rewatched season 3 on Netflix (love not having to deal with the commercials) and I have to say I really enjoyed the season. Yes, there were silly plot deficiencies with respect to instantaneous switching from vulnerable Humans to invulnerable Kryptonians, but over all I loved the pacing and how the story of the Dark Kryptonians slowly unfolded.
For example, having broken hearted Kara distancing herself for months from her sister Alex and from her best friend, Lena.
How we saw Kara's healing begin before Mon'el returned when she began supporting Alex through her own relationship meltdown.
Then there was the "distraction" of Morgan Edge in the first half of the season ....
...as they insinuated Sam and eventually Reign into our consciousness was neat.
James, Winn, Cat and now Sam all know Kara is adopted, but does Lena?
I wonder if next year, the writers will recall the Alura / Alex greeting at the DEO. We / I complained that Lena was too close when Supergirl introduced Alex to her mom, fearing that she just outed herself to Lena.
But Lena has her own healthy (?) dose of hubris. If she heard the exchange / saw the hug Lena probably assumed that Alex and Kara Danvers' family adopted the Kryptonian and that was how Kara and Supergirl were so close. (Recall SG told Lena she was having coffee with Kara when the CEO called Kara that night the bad guys tossed Lena off the balcony. )
I can see Lena confronting Kara &/or Alex about the secret during an argument about whether Lena could trust Supergirl again, perhaps after the Russian Supergirl is revealed.